The use of solid red phosphorus as a controlled source of P.sub.4 gas in various deposition processes presents severe problems due to (a) the multiphasic nature of commercial red phosphorus; (b) the resultant variability of equilibrium vapor pressure and other thermodynamic properties; (c) thermal instability of red phosphorus (e.g. multiple phase transitions); and, (d) the slow kinetics of vaporization of red phosphorus.
For example, in the temperature range of 300.degree.-400.degree. C., the time required for red phosphorus to reach its equilibrium vapor pressure is about 20 hours. Thus, for the first 20 hours of any deposition at a constant temperature the gas produced from a phosphorus generator will be changing. This makes it very difficult to produce P.sub.4 gas from red phosphorus at a constant rate. For optimum control of the process, One either has to try to vary the temperature in some way during the initial heating of the phosphorus in an attempt to produce P.sub.4 at a constant rate or one must wait the 20 hours for the phosphorus to reach its equilibrium vapor pressure, before doing any deposition.
Vacuum evaporation processes are disclosed in the above-identified co-pending applications entitled VACUUM EVAPORATED FILMS OF CATENATED PHOSPHORUS MATERIAL, THERMAL CRACKERS FOR FORMING PNICTIDE FILMS IN HIGH VACUUM PROCESSES, and HIGH VACUUM DEPOSITION PROCESSES EMPLOYING A CONTINUOUS PNICTIDE DELIVERY SYSTEM. The latter two applications also disclose molecular beam deposition (molecular beam epitaxy) apparatus. These earlier applications either use a heated generator containing red phosphorus or utilize a carrier gas passing through heated white phosphorus to produce the P.sub.4 gas when required.
As disclosed in the prior above-identified application entitled SPUTTERED SEMICONDUCTING FILMS OF CATENATED PHOSPHORUS MATERIALS AND DEVICES FORMED THEREFORM, it has been found that using pure KP.sub.15 as a sputtering target produces potassium-rich depositions due to the high volitility of phosphorus.